package com.lagou.sqlSession;

import com.lagou.pojo.Configuration;
import com.lagou.pojo.MappedStatement;

import java.lang.reflect.*;
import java.util.List;

public class DefaultSqlSession implements SqlSession{
    private Configuration configuration;

    public DefaultSqlSession(Configuration configuration) {
        this.configuration = configuration;
    }

    @Override
    public <E> List<E> selectList(String statementId, Object... params) throws Exception {

        //将要物完成对simpleExecutor里的query方法的调用
        SimpleExecutor simpleExecutor = new SimpleExecutor();
        MappedStatement mappedStatement = configuration.getMappedStatementMap().get(statementId);
        List<Object> list = simpleExecutor.query(configuration, mappedStatement, params);

        return (List<E>)list;
    }

    @Override
    public <T> T selectOne(String statementId, Object... params) throws Exception {
        List<Object> objects = selectList(statementId, params);
        if(objects.size()==1){
            return (T)objects.get(0);
        }else {
            throw new RuntimeException("查询结果为空或返回结果过多");
        }

    }



    @Override
    public int update(String statementId, Object... params) throws Exception{
        SimpleExecutor simpleExecutor = new SimpleExecutor();
        MappedStatement mappedStatement = configuration.getMappedStatementMap().get(statementId);
        int a = simpleExecutor.update(configuration, mappedStatement, params);
        return a;
    }



    @Override
    public <T> T getMapper(Class<?> mapperClass) {
        //使用jdk动态代理为Dao接口生成代理对象并返回
        Object o = Proxy.newProxyInstance(DefaultSqlSession.class.getClassLoader(), new Class[]{mapperClass}, new InvocationHandler() {
            @Override
            public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
            //proxy  当前代理对象的引用
            //method 当前被调用方法的引用
            //args 传递的参数

            //准备参数 1 statementId:namespace.id
            String methodName = method.getName();
            String className = method.getDeclaringClass().getName();
            String statementId = className+"."+methodName;

            //准备参数 2 params:args

            //获取被调用方法的返回类型
                Type genericReturnType = method.getGenericReturnType();
                //判断是否进行了泛型类型参数化
                if(genericReturnType instanceof ParameterizedType){
                    List<Object> objects= selectList(statementId,args);
                    return objects;
                }else if(genericReturnType.toString().equals("int")){
                    int row = update(statementId,args);
                    return row;
                }
                return selectOne(statementId,args);

            }
        });

        return (T) o;
    }
}
